Preheat oven to 375ºF. Line two large baking sheets with parchment paper.
In a large bowl, melt the butter and let it cool.
1 cup Unsalted butter
Place a layer of paper towels on a large plate, and spread the pumpkin puree out on the paper towels. Place another layer of paper towels on top of the pumpkin and press gently. Change the paper towels every 5 minutes over the next 15 minutes. You should now have 1/2 cup of drained pumpkin puree.
1 cup Pumpkin puree
In a medium mixing bowl, whisk together the flour, baking soda, cream of tartar, pumpkin pie spice, and kosher salt.
2 1/2 cups All-purpose flour, 1 tsp Baking soda, 1 1/2 tsp Cream of tartar, 2 1/2 tsp Pumpkin pie spice, 1/2 tsp Kosher salt
In a large bowl, whisk the cooled butter, granulated sugar, and dark brown sugar together at least 1 minute. Whisk in the pumpkin puree, egg yolk, and vanilla extract. Gradually fold the dry ingredients into the wet ingredients just until combined.
1 large Egg yolk, 1 cup Granulated sugar, 1/4 cup Dark brown sugar, 1 1/2 tsp Vanilla extract
In a small bowl, stir together the 1/4 cup of granulated sugar and 1 1/2 teaspoons of cinnamon. Scoop 2 tablespoons of cookie dough, roll into a ball, and roll in the cinnamon sugar. Place the cookie dough balls 2 inches apart on the prepared baking sheet. Gently press the dough ball down slightly with your fingers.
1/4 cup Granulated sugar, 1 1/2 tsp Ground cinnamon
Bake for 8-11 minutes, until the edges are set and golden. Allow to cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.